Hey Allen: Why would my P0420 be disabled?

[MikeGyver]

So as to not hijack the DTCs thread, I started this one. P0420 and P0430 are both set to show no SES and no error reported. Was this in your original tune?

[farmtruc]

Those are cat efficiency codes, do you have any rear o2's on the truck.
Also, on some of the HD trucks, this code isn't on from the factory.
Take this 2000 HD truck file for example, it's all stock and doesn't have those codes on, so yours is the same.

http://www.ls1truck.com/newstorage/temp/flash.hpt

[MikeGyver]

I see, from the factory. Yeah, I have rear O2s, if I enable the codes, will I be able to test my cats? Or do blown vehicles automatically think that the cats are bad because they can't flow enough?

[farmtruc]

IF they were off in the stock calibration, then the truck will pass all emissions and Ready State Tests.
it's ok to have cats with a blower.

[MikeGyver]

No, I mean I just want to know if I can use it to find out if my cats are plugging up.

[farmtruc]

No, I mean I just want to know if I can use it to find out if my cats are plugging up.

I'm not sure becuase they weren't on from the factory, so there may be other values that need to be changed.
Best to just inspect them, the rear o2's aren't always accurate.

[MikeGyver]

Oakie-dokie. Thanks.

[GasGuzzler]

The DTC's P0420 and P0430 do not mean the converters are plugged. For that test, you need an exhaust backpressure gauge. The DTC's mentioned are to report when the precious metals in the converter have degraded beyond the point where they no longer remove enough pollutants.

[MikeGyver]

I wish I had a pressure gauge from the start for something to compare to.
I guess I didn't think about what efficiency meant, only being able to think like a gearhead. I get it now, though: why would GM give a darn if my catalytic converters are plugged up, as long as it meets emissions standards.

[GasGuzzler]

GM doesn't really care if they're plugged up. GM only cares if they pass EPA and CARB standards which is what the 420 and 430 diagnostics are supposed to "prove". The only thing that happens with a clog is poor or NO performance, not 420 and 430. These codes do not mean the cats are plugged, it's means they don't work.